1. Field of the Invention
This invention relates to a mobile machine, in particular an industrial truck or a fork lift truck, having a chassis and an operator""s cab located on it by a suspension system.
2. Description of the Prior Art
Operators of mobile machines are frequently subjected to significant vibration stresses because the machines are not equipped with a suspension system. Fork lift trucks in particular normally have no suspension elements between the frame and the chassis. When the mobile machine travels over bumps or depressions, whole-body vibrations can be transmitted to the driver. These vibrations are then damped only by the driver""s seat. In machines of the prior art, the operator""s cab is mounted on steel-rubber bearings, which of course reduces the vibration load to some extent, but still lets through significantly more vibrations for the driver than are desirable.
Cabs mounted on suspension systems have recently become common on utility vehicles and agricultural tractors.
The journal xe2x80x9cNoise and Vibration Worldwide,xe2x80x9d November 1997, pages 17 to 26, contains a scientific article on the development of suspended cabs for fork lift trucks. In the right-hand column on page 22, the above referenced article proposes replacing the four steel-rubber bearings that normally connect the cab with the chassis with four metal springs and shock absorbing elements. One embodiment of this suspension system is illustrated in FIG. 5 on page 24. The suspension system proposed in the above-referenced article significantly damps the vibrations that are transmitted to the driver""s cab, although an even more effective damping of impact loads would be desirable.
The object of the invention is therefore a mobile machine in which the impact load on the operator""s cab is reduced even further.
The invention teaches a mobile machine having a chassis and an operator""s cab located on it, in which there are one or more pneumatic or hydropneumatic suspension elements between the chassis and the operator""s cab.
The use of a pneumatic or hydropneumatic suspension system significantly reduces the vibration load exerted on the operator. The driver""s comfort, while operating the machine, is increased significantly. The expected result is a decrease in injuries to the driver""s spinal column. There is also reason to expect an increase in productivity as a result of the greater feeling of well being on the part of the operator.
In one embodiment of the invention, the operator""s workplace, or the driver""s cab, is guided in the vertical direction by guide elements and is supported on one, two or more cylinders filled with one or two fluids. The guide elements used can be either conventional linear guides such as slides, roller guides, circulating ball guides, and dovetail guides or lifting platform guides. If the travel of the cab is not particularly long, guides consisting of leaf springs or movable arms, for example of the type used on sliding lattice grates, can also be used. Guides on levers or connecting rods can also be used, of the type widely used in the design of suspended chassis of motor vehicles. The fluid is initially pressurized by an adjustable-pressure reservoir unit. The initial pressure can be set to the desired level and thereby adjusted to the weight of the driver. The use of a hydropneumatic suspension system also makes it possible to adjust the height of the cab, and is recommended in particular for use on fork lift trucks, because on these vehicles there is generally already a hydraulic pump that provides sufficient hydraulic pressure.
In one embodiment of the invention, there is an adjustable throttle in the fluid line between the cylinder and the reservoir element, in which case the system consisting of the cylinder, reservoir and throttle represents a spring-mass-damper system, in which the stiffness of the spring can be adjusted by the initial pressure in the reservoir unit, and the damping can be modified by adjusting the cross section of the throttle. This spring-mass-damper system can be adapted to the different cab models or to different driver weights by modifying the initial pressure and the cross section of the throttle. The operator""s cab can then be moved up and down by several centimeters, for example, and is effectively suspended by the system described above.
In an additional embodiment of the invention, there can be an active regulation of the suspension system. A system of sensors in the machine can record the operating conditions, and a closed-loop control system continuously sets and adjusts the optimal parameters for the suspension system (initial pressure in the reservoir and throttle cross section). This system further increases the quality of the ride in the vehicle during travel and operation.